mac: Support ARCHS with zero or one element in the make and ninja generators.

pylib/gyp/xcode_emulation.py

Index: pylib/gyp/xcode_emulation.py
===================================================================
--- pylib/gyp/xcode_emulation.py	(revision 1197)
+++ pylib/gyp/xcode_emulation.py	(working copy)
@@ -277,7 +277,6 @@
     self._Appendf(cflags, 'MACOSX_DEPLOYMENT_TARGET', '-mmacosx-version-min=%s')
 
     # TODO:
-    self._WarnUnimplemented('ARCHS')
     if self._Test('COPY_PHASE_STRIP', 'YES', default='NO'):
       self._WarnUnimplemented('COPY_PHASE_STRIP')
     self._WarnUnimplemented('GCC_DEBUGGING_SYMBOLS')
@@ -288,10 +287,12 @@
     self._WarnUnimplemented('MACH_O_TYPE')
     self._WarnUnimplemented('PRODUCT_TYPE')
 
-    # TODO: Do not hardcode arch. Supporting fat binaries will be annoying.
-    # Even if self._Settings()['ARCHS'] contains only a single arch, dependent
-    # targets might have been built with a different single arch.
-    cflags.append('-arch i386')
+    archs = self._Settings().get('ARCHS', ['i386'])
+    if len(archs) != 1:
+      # TODO: Supporting fat binaries will be annoying.
+      self._WarnUnimplemented('ARCHS')
+      archs = ['i386']
+    cflags.append('-arch ' + archs[0])
 
     cflags += self._Settings().get('OTHER_CFLAGS', [])
     cflags += self._Settings().get('WARNING_CFLAGS', [])
@@ -393,8 +394,12 @@
                      '-Wl,' + gyp_to_build_path(
                                   self._Settings()['ORDER_FILE']))
 
-    # TODO: Do not hardcode arch. Supporting fat binaries will be annoying.
-    ldflags.append('-arch i386')
+    archs = self._Settings().get('ARCHS', ['i386'])
+    if len(archs) != 1:
+      # TODO: Supporting fat binaries will be annoying.
+      self._WarnUnimplemented('ARCHS')
+      archs = ['i386']
+    ldflags.append('-arch ' + archs[0])
 
     # Xcode adds the product directory by default.
     ldflags.append('-L' + product_dir)